1. Field of the Invention
This invention relates to precisely controlled heat transfer devices and methods, which are particularly useful in medical applications requiring limited heat ranges.
2. Description of the Prior Art
Processes which require closely regulated heat typically rely on thermostatically controlled electrical resistance units and sophisticated safety relief valves and back-up systems. A controlled maximum temperature is desirable in many applications including medical treatment, welding of plastics, heat treatment of metals and the like.
Since heat can easily damage living tissue, many medical uses require means to limit heat transfer to avoid reaching temperatures which would otherwise cause harm. For example, paraffin baths and water vaporization devices may potentially reach unacceptable, dangerous temperature levels.
Traditional means of limiting heat transfer have several defects. Thermostatically controlled electrical resistance units such as heating pads vary substantially across their faces; a 15 to 20 degree Fahrenheit variation is quite common. Thermostatic control is difficult and expensive when applied in constricted places, such as the external ear canal. The transfer of heat by pumping thermostatically controlled electrically heated liquid through devices such as the aqua-K heating pad gives uniform control but it is quite expensive. This method does not adapt itself readily to confined spaces, since the liquid is difficult to force through a narrow passage at sufficient speed to make up for heat loss.
Other medical applications of heat transfer include the use of paraffin baths for heat treatment of arthritic joints. Paraffin baths require a large volume of paraffin which must be constantly heated to maintain its temperature. Paraffin is messy and coats any item placed within the bath. The baths are dependent on thermostatic heating controls to maintain a safe temperature. A stuck thermostat valve may result in excessively high temperatures. Such systems may result in heat damaged material or even in physical injury to a patient. Thermostatic control of temperature does not provide the safety required in such applications.
3. Brief Summary of the Invention
The limited heat transfer devices of the invention supply and provide vaporized liquid as a source of heat for heat transfer. A liquid is chosen with known boiling point and is placed within a suitable reservoir. The liquid is then heated to its vaporization point resulting in vapor having a known temperature. The temperature may be altered within the same liquid merely by altering the pressure of the system. Since pressure, volume and temperature are related by the formula PV=nRT, a change in pressure results in temperature change if the other variables remain fixed.
The vapor, while hot, represents the maximum temperature available under the system. The vapor is at a controlled upper temperature limit when it escapes from the reservoir as long as there is a source of liquid. The vapors are then directed through suitable conduits to a terminal area where accurately controlled heat transfer takes place.
While the device is useful for any application requiring heat transfer with closely regulated temperature and a maximum safety temperature, several embodiments are illustrated below.
One terminal area is designed to produce physical therapy results for the same purpose but to a better degree than paraffin baths, contrast baths and hot compresses. Vapor is introduced into a physical therapy terminal which comprises an enclosure designed like a glove box. A "glove" of thin plastic or rubber forms part of the enclosure such that a hand or other extremity thrust into the glove may be heated by vapors within the enclosure and exterior of the glove without contacting the vapors themselves.
Condensation occurs in an exothermic reaction over the entire affected surface of the glove, bringing the temperature to a uniform level at approximately the condensation point of the heat transfer material. As the condensate collects it is ultimately drained out through an outlet which may be connected to a return source of the heat transfer liquid.
A heating pad or hot compress terminal comprises an air mattress-like enclosure with a vapor inlet and a vapor outlet which are separated by seals. A valve produces a mild pressure backup to maintain vapor within the enclosure under slight pressure so that the passages remain expanded. A high degree of safety is achieved through the use of the closely controlled temperatures of the invention.
An ear wax removing terminal includes adjustable stop and gentle pressure applying members. Tubing is connected to the vapor supply for transmitting vapor to a tip portion which contacts excess cerumen in the external auditory canal. The controlled heat provided melts the wax plug allowing easy removal. Removal is accomplished by aspiration, absorption or by entrapment utilizing a retractable member adjacent the tip portion.
In any of the devices utilizing vapor heat transfer, an element for condensing surplus vapor may be added if the vaporization liquid is costly or hazardous.
A body cavity terminal for heat treatment of cavities including the vagina, rectum and the outer ear canal includes a vapor-tight, thin walled bag. Tubing is connected to the vapor supply for transmitting vapor to the bag for heat transfer. A vapor return tube with valving to allow the maintenance of low pressure to inflate the bag is connected to the condensation unit or allowed to escape to the air if the vapor is safe and inexpensive. Terminals intended for rectal use preferably have a narrow constriction to avoid discomfort within the anal canal.
Utilization of the heat transfer devices of the invention results in a clean, safe transfer of heat to the desired area. The use of vapors limits the maximum temperature obtainable and eliminates the need for thermostats and alarm and automatic shut-off systems.